1 purva means one unit of the ancient Jain scriptures called Purvas. Purvas are considered among the oldest Jain treatises and were part of the original Drstivāda (12th Anga). Each Purva is a distinct branch of knowledge (philosophy, cosmology, ethics, etc.). Today the Purvas are regarded as lost in both Śvetāmbara and Digambara traditions, and only later works summarize or reference their ideas. Different Jain traditions sometimes list varying numbers and names for the Purvas, but the general idea remains: 1 purva is one of these very ancient, foundational texts of Jain doctrine. You can read more here